UGRANDITE :

Name given to a group of garnets comprising andradite, grossular and uvarovite .

UIGITE :

- variety of nephrite, banded, of yellow and white colour, from Uig, Skye Island in Scotland

 (Eppler)

- variety of chlorastrolite banded, of yellow and white colour, from Uig, Skye Island in Scotland ( Schlossmacher )

UINTAHITE or UINTAITE :

Variety of asphalt used for ornamental objects (from Uinta -Valley, Utah ) .

Equally used as a Prohibited Appellation for jet .

Colour : brilliant black

Hardness : 2 to 2.5

Density : 1.035 to 1.070

ULTRALITE :

Commercial name for a synthetic sapphire of violet-red colour .

ULTRAMARINE :

Synonym for outremer .

Designates generally artificial lazurite or its components .

UMINA :

Inca name for emerald .

UNAKITE or UNACITE :

Etym. from Unaka in North Carolina in U.S.A.

Variety of massive epidote, of green colour with pink inclusions of feldspath and milky ones of quartz or of mica .

UNACHTER LASURSTEIN :

German name for klaprothine .

UNGHWARITE or UNGHVARITE :

Synonym for Chloropal .

UNIONITE :

Variety of zoisite .

UINITAITE :

Variety of Uintaite .

UNRIPE AMBER :

Old English name; prohibited appellation for gedanite .

UNRIPE DIAMOND :

Old prohibited appellation for a rock crystal or a colourless zircon .

UNRIPE RUBY :

Old prohibited appellation for a red zircon .

UPALA :

From Sanskrit : precious stone : designates generally opal ( the name opal being derived from it).

UPARATNANI :

Hindou name for the 4 lesser gems of the Nauratan, being hyacinthe (zircon/ red hessonite garnet), yellow sapphire /topaz, cat’s eye and coral .

URALIAN CHRYSOLITE :

Prohibited appellation for a demantoid garnet .

URALIAN EMERALD:

Prohibited appellation qui designating a green andradite garnet  from Nijni-Tagilsk, URSS. Sometimes called " Garnet from Bobrovska ".

URALIAN OLIVINE :

Prohibited appellation for a demantoid garnet .

URALIAN SAPPHIRE :

Prohibited appellation for a blue tourmaline .

UTAH JET :

English name given to a jet of inferior quality from Wayne County, Utah, USA .

UTAHLITE :

Variscite found as nodular masses in Toole County, Utah, USA .

Or term used to designate or a variscite or a turquoise still embedded in its mother rock .

UTAH TURQUOISE :

Prohibited appellation for a variscite .

UVAROVITE :

Etym : dedicated to the Russian minister Ouwarow .

Variety of garnet

(SiO4)3Ca3Cr2

Physical and optical properties :

- Colour : green to dark emerald green

- transparency : translucent to opaque

- Hardness : 7 to 7.5

- S.G. : 3.41 to 3.52

- R.I. : 1.838 to 1.87

- Dispersion : 0.014 to 0.021

- System cubic

UWAROWIT:

German name for uvarovite